For TIME’s May 21 cover story (available to subscribers here), I explored the personal history and legacy of Dr. Bill Sears, the father of a child-rearing philosophy called attachment parenting. As the author of 40-plus books on parenting and pregnancy, Sears is a familiar figure to many American mothers and fathers. Some parents subscribe to his theory that attachment parenting — characterized by extended breast-feeding, co-sleeping and wearing your baby in a sling across your body — is the best way to raise confident, secure children. Others think Sears is an antifeminist tyrant, or that his ideas are just totally unrealistic.

Sears’ most well-known parenting manual, a purple 767-page tome called The Baby Book, is ubiquitous, but his own story is not. In reporting this article for TIME, I was intrigued to find out how little had been written about Sears’ upbringing or how he came up with his parenting theories in the first place.

It turns out that he and his wife Martha had written a lot of earlier books about attachment parenting before The Baby Book, including one with an evangelical approach. I also came across a book the Searses wrote in 1982 based on another book called The Continuum Concept, which I traced back to a college dropout who had become fascinated by child care in the Venezuelan jungle. “We read the book and thought, Well, this is neat,” says Sears.

When I interviewed Bill and Martha Sears at their home in Southern California, we talked for a long time about their childhoods — neither of which resembled the kind of idealized environment the couple imagines for their supporters. Bill’s father abandoned him when he was a baby; Martha’s father died when she was young, and her mother suffered from mental illness. Their childhoods seemed to be lacking in affection and parental bonding, the very tenets of their teachings.

I began to realize that Bill Sears’ theories are based not only on his experience as a pediatrician and father, as most of his readers assume, but also on the work of others and on the Searses’ own upbringings as Midwestern Catholics. Martha acknowledged this in our interview: “You could say I’m reacting to my background.”

As I spoke with parents, especially mothers, about their parenting styles, I found that even those who didn’t know Bill Sears by name had been touched by the phenomenon of attachment parenting — whether as practitioners of some of its tenets or as critics. TIME’s May 21 cover story introduces readers to Sears, the man whose influence has shifted mainstream American parenting and brought us to a point where mothering requires more physical and emotional investment than perhaps ever before.